Synthesis characteristics of NH4-[B]ZSM-5 in the presence of fluoride ions

Abstract

NH₄-[B]ZSM-5 is synthesised directly from a non-alkaline medium in the presence of fluoride ions. By influencing the equilibration of reactants, the fluoride ions control the crystallisation rate of the zeolite, affect the framework composition (Si/B ratio) of the products and promote crystal growth along the c axis direction of the zeolite MFI structure. Preferential crystallisation of silica-rich products is observed when higher concentrations of fluoride ions are present in the reaction mixtures. Increased dilution of reaction mixtures results in more elongated crystals with reduced boron substitution. A composition diagram of reaction mixtures for synthesis of NH₄-[B]ZSM-5 is presented.